1. Field of the Invention
This invention relates to lights that use multiple light-emitting diodes, as well as to fixtures for mounting such lights.
2. Description of the Related Art
Incandescent light bulbs are commonly used for indicator lamps, task lamps, general lighting, decorative lamps, warning lamps, traffic lamps and the like. However, incandescent bulbs, and to a lesser extent even plasma-based fluorescent and halogen lights, are generally inefficient in terms of energy use and are subject to frequent replacement due to their limited lifetime. Significant savings can be made by the use light bulbs where the source of light is light-emitting diodes (LED).
LEDs are much more efficient (in terms of lumens per watt) than incandescent and fluorescent lights; moreover, LEDs generally last much longer. This is particularly true of the class of LEDs known as “super-luminescent” or “super-bright,” which have already found uses in such applications as automobile tail lights and traffic signal lights.
Being diodes, one problem with LEDs is that they are direct-current (DC) devices that are easily damaged by too high reverse voltage, whereas the power supplies for many devices that would benefit from the advantages of LEDs deliver alternating current (AC). Even low-voltage light fixtures typically use a 12V AC power source, which is transformed from, for example, 120V AC at 60 Hz.
One common way to provide direct current to LEDs from an AC source is to include in the power-supply circuit a full-wave rectifier and a current-limiting device such as a power resistor. One drawback of this approach is that four rectifying diodes are typically needed and each of these rectifying diodes must carry half the full current load of all the LEDs.
Another known way to provide DC current to LEDs is to include in the power-supply circuit a half-wave rectifier and, again, a current-limiting device such as a power resistor. This is a much simpler circuit than is needed for full-wave rectification, but even it has at least three major drawbacks: First, the light emitted from the LEDs will flicker, for example, at 120 Hz in case the AC power source frequency is 60 Hz. Second, when the supplied voltage is negative, this circuit assumes that the LEDs will evenly divide the reverse voltage among themselves. Failure to do so can lead to a cascade failure of the LEDs; this failure is most prominent in transient conditions. Third, the rectifying diode must carry the full current load of the LEDs.
Even assuming that the power supply problems of the LEDs are overcome, there must still be some convenient way to mount and install the lights themselves. There are of course many different types of light fixtures for the many different common types of incandescent light bulbs. These fixtures feature an array of different types of physical connections with wedge, screw-in, bayonet, flange, bi-pin and other bases. This means that any after-market LED-based light bulb replacement must be able to correctly connect to the different types of existing sockets of the bulbs it is intended to replace. It would be possible to mount LED units within the casings—usually bulbs—of the original lights, but this complicates the manufacture of such LED replacements.
Yet another concern is that incandescent elements can typically be mounted without regard to polarity, whereas existing LED arrangements cannot. When installing an LED replacement in a DC system such as an automobile tail light, there is therefore a risk of incorrect installation because even with a given fitting, the polarity of the wiring is not always the same from one car manufacturer to another.
What is needed is an LED lighting arrangement that eliminates or at least reduces the problems mentioned above. Furthermore, some fitting is needed to enable easy after-market LED replacement. This invention provides such an arrangement and fitting.